Question

Smallest reflex consists of (a) Afferent neuron (Receptor) (b) Efferent neuron (effector or excitor) (c) Both (a) and (b) (d) None of these

Short answer

(c) Both (a) and (b)

Step-by-step solution

Identify the components of a reflex arc

A reflex arc is a neural pathway that controls reflex actions. This pathway involves several components including a sensory receptor, an afferent neuron, Interneuron (not in all reflexes), an efferent neuron and an effector.

Examine the choices given in the exercise

The exercise presents 4 choices: (a) Afferent neuron (Receptor), (b) Efferent neuron (effector or excitor), (c) Both (a) and (b), (d) None of these. Based on the understanding from Step 1, we know that reflex arc, which is the smallest unit of a reflex, comprises of both afferent and efferent neurons. So, choices (a) and (b) can't alone constitute the smallest reflex as both are integral components.

Select the correct answer

Given the analysis in the previous steps, the correct answer is (c) Both (a) and (b). This includes both the afferent (sensory) neuron and the efferent (motor) neuron which constitute a complete reflex arc - the smallest reflex.

Key concepts

Afferent Neuron

An afferent neuron plays a crucial role in the reflex arc by transmitting sensory signals to the central nervous system (CNS). These neurons are often known as sensory neurons because they carry sensory information from external stimuli.
When you touch a hot object, for example, afferent neurons are responsible for sending the sensation of heat to your brain quickly. This is how your body realizes that it's touching something hot and potentially harmful.
Key points about afferent neurons include:

• They transmit sensory information from receptors to the CNS.
• Their cell bodies are located in the dorsal root ganglion of the spinal cord.
• Afferent neurons have long dendrites that connect directly to sensory receptors.

Effectively, all messages coming into the CNS come via afferent neurons, making them a critical part of the sensory pathways in reflex actions.

Efferent Neuron

Efferent neurons, often referred to as motor neurons, play a vital role in the reflex arcs by carrying signals from the CNS to the effector organs. These neurons are responsible for producing a response as they directly control muscles and glands. In simpler terms, they send the action commands that cause muscles to move or glands to release hormones.
Consider the example of touching something hot as mentioned earlier. While afferent neurons send the initial warning signal to the CNS, efferent neurons execute the body's "pull away" response.
Highlights about efferent neurons:

• They conduct signals away from the CNS towards effectors, like muscles and organs.
• They are essential for enabling motor responses to signals from the brain.
• Their cell bodies are typically located within the spinal cord or cranial nerve nuclei.

The smooth operation of the reflex arc heavily depends on the quick and efficient functioning of efferent neurons, translating neural signals into tangible actions.

Components of Reflex Action

Reflex actions are quick, automatic responses to specific stimuli that don't require conscious thought. They help protect the body by enabling a rapid response to potentially harmful situations. The reflex arc, being a fundamental part of reflex actions, consists of several interconnected components.
The main components include:

• Sensory Receptor: Detects the stimulus and generates a sensory impulse.
• Afferent Neuron: Carries sensory information to the CNS.
• Interneuron: In many reflex arcs, it acts as a relay, transmitting signals between afferent and efferent neurons. Often present in more complex reflex actions.
• Efferent Neuron: Sends processed instructions from the CNS to the effector.
• Effector: The part of the body that responds, such as a muscle contracting.

Understanding that a reflex action is based on this simple pathway helps us appreciate how our bodies handle immediate threats effectively. Each component's role, from detection to reaction, highlights the complexity and efficiency of our nervous system.